This invention relates to an optical positionalignment system for processing minute materials.
The theory, that Moire signals obtained from the light passing through or reflected from a pair of diffraction gratings can be applied to measuring and controlling the displacement of their relative positions, has been proposed by J. Guild in Diffraction Gratings as Measuring Scales issued by Oxford U.P. in 1960.
As one of the prior arts in regard to the alignment method by using the theory, there is means to control and reduce Moire signals to a minimum value. However, this means can obtain only restricted accuracy of the alignment because the art makes the alignment by using the point where the signal is naught with respect to the setting position.
As another prior art in regard to the alignment method by using the same theory, there is means to compare .+-. 1st order diffraction signals of Moire signals. Indeed this means can increase the alignment accuracy up to 20 nm by combining the technique of splitting two bundles of light and receiving the emitted modulation signals with the prior art, however the higher accuracy of alignment might be desired.